Computer Networks (CIDR) Interview Guide

🟢 Easy (Basics)

1. CIDR?

IP/prefix notation (e.g., 10.0.0.0/16) defining network size.

2. Private IPv4?

10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.

3. Subnetting?

Borrow host bits to create subnets; adjust prefix length.

4. VLSM?

Different prefix lengths to optimize allocation.

5. Hosts per /24?

254 usable (256 − network − broadcast).

1. Summarization?

Advertise an aggregate to shrink routing tables.

2. NAT types?

SNAT/DNAT/PAT translating addresses/ports.

3. ACL vs SG?

ACLs stateless order‑matched; SGs stateful allow rules.

4. Overlap?

Overlapping CIDRs break peering/VPNs; avoid by planning.

5. IPv6 basics?

/64 LANs, huge space, SLAAC, no NAT required.

1. Hub‑spoke cloud.

Central hub with firewalls; spokes per app; non‑overlapping CIDRs; shared services.

2. BGP with on‑prem.

Dynamic route exchange for hybrid links.

1. Need 4 equal subnets from /24.

Use /26 (64 each) → 4 subnets.

2. Peering overlap fix.

Renumber or NAT one side; renumber preferred for simplicity.

3. Global plan.

Allocate /16 per region; /20 per env; leave growth buffer.

Generated for quick interview revision — basics, hands-on, advanced, and scenarios.